Ping: RFR(s-m): 8218988: Improve metaspace verifications

[Thomas Stüfe]

Hi all,

I'd love to get a second pair of eyes on this. Zhengyu already reviewed;
submit tests ran thru; patch is active in our nightlies w/o problems; I see
no regressions in the jtreg tests vulnerable to metaspace performance (e.g.
SelectionResolution).

Latest webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8218988--improve-metaspace-verifications/webrev.01/webrev/

Bug: https://bugs.openjdk.java.net/browse/JDK-8218988

Thanks & Best Regards, Thomas


On Fri, Feb 15, 2019 at 11:12 AM Thomas Stüfe <thomas.stuefe at gmail.com>
wrote:

> Hi all,
>
> may I please have reviews for the following change:
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8218988
> cr:
> http://cr.openjdk.java.net/~stuefe/webrevs/8218988--improve-metaspace-verifications/webrev.00/webrev/
>
> In short, this reworks metaspace verifications.
>
> Thorough verifications were added for JDK-8198423, but turned out too slow
> in general, so were made switchable later (-XX:+VerifyMetaspace) with a
> switch which is usually off. However, it would be good to have these
> verifications at least sometimes, so this patch changes VerifyMetaspace
> from a boolean to an interval which causes verifications every n passes
> thru a verification callsite. The default is 500, which does not slow down
> metaspace-heavy tests like SelectionResolution noticably.
>
> This patch also contains a number of cleanups and simplifications. In
> particular:
>
> class ChunkManager:
>
> - removed sum_free_chunks(), sum_free_chunks_count(),
> locked_verify_free_chunks_total() and locked_verify_free_chunks_count().
> These functions were used to validate the counters in ChunkManager. But
> this way was inefficient, since we walk the lists twice. The counter
> validation is now done in ChunkManager::verify() and only requires one list
> walk. Also, less code.
> - Now we only have one verification function left, ChunkManager::verify().
> To distinguish between quick counter verify and deep costly verify, I gave
> it a "bool slow" argument.
> - all verifications are now #ifdef ASSERT. In fact, they were before too
> since we used assert() inside the verification functions.
> - expensive verifications are now done depending on
> VerifyMetaspaceInterval.
> - I removed expensive verifications from some hot paths (e.g.
> ChunkManager::chunk_freelist_allocate). Verifications are now done only
> when interesting things happen: chunk fuses or splits, or a Classloader
> died and releases its SpaceManager.
>
> minor stuff:
>
> - made getters for counters (free_chunks_total_words(),
> free_chunks_total_bytes(), free_chunks_count()) inline
> - removed locked_print_sum_free_chunks(), which was nowhere used.
> - constified versions of free_chunks() and humongous_dictionary()
>
> class VirtualSpaceNode:
>
> - removed container_count_slow() and verify_container_count() since it
> duplicates the verifications we do in VirtualSpaceNode::verify().
> - similar to ChunkManager, gave VirtualSpaceNode::verify a "bool slow"
> parameter to distinguish between quick and thorough verification.
> - modified VirtualSpaceNode::verify_free_chunks_are_ideally_merged() to
> print out a map of the node if it fails, before asserting.
>
> Miscellanous:
>
> - added some new internal counters to the statistic (see
> metaspaceCommon.hpp)
>
>
> Gtests: test_virtualSpaceNode.cpp
>
> - renamed ChunkManagerTest to ChunkManagerTestAccessor to make its
> (narrow) intent clearer
> - removed parts which had been commented out since chunk coalescation
> (8198423) and which would never really work, plus code which relied on it.
>
> Note: IMHO the value of these tests is a bit diminished and probably not
> worth the trouble of maintaining? To compensate for that I did add
> test_metaspace_allocation.cpp some time ago which is more thorough and less
> vulnerable against changes in the metaspace implementation.
>
> ----
>
> Tests: I stressed my patch locally (linux x64) with my own metaspace tests
> as well as hotspot/jtreg/runtime/*, including the SelectionResolution
> tests. Before pushing, I will put the patch through our nightlies.
>
> Thank you, Thomas
>
>
>
>
>